Photoacoustic tomography (PAT) is an emerging non invasive imaging technique, photoacoustic imaging, where the imaging is in three dimensions. A radiation of pulsed electromagnetic waves irradiates a target object causing local thermal expansion and concomitant generation of sound waves. The sound waves can be detected by an ultrasonic detector placed outside of the object being imaged and an image of the object can further be obtained according to the recorded acoustic signals produced by the sound waves. PAT combines the advantages of optical absorption contrast with high resolution of ultrasound. Materials with favorable photoacoustic properties can be used to improve contrast for deep target imaging. Gold nanoshells and some other metallic nanomaterials are being researched for application in PAT, such as that described in U.S. Pat. App. No. 2005/0175540. However, these metallic nanomaterials are inherently toxic, not biodegradable or their fate in the body in not currently completely understood. Accordingly, there remains a critical need for a novel material that can improve photoacoustic properties while being non-toxic, biocompatible and biodegradable.